Every base 4 digit of n is a base 10 digit of n.

Terms

a(0) =1a(1) =2a(2) =3a(3) =13a(4) =21a(5) =31a(6) =42a(7) =63a(8) =102a(9) =123a(10) =203a(11) =213a(12) =231a(13) =234a(14) =235a(15) =238a(16) =239a(17) =341a(18) =351a(19) =381a(20) =421a(21) =520a(22) =682a(23) =1013a(24) =1023a(25) =1024a(26) =1025a(27) =1026a(28) =1028a(29) =1029